1. Field of the Invention
The present invention relates to a belt sander, and more particularly to a belt sander for delivering a workpiece at a constant speed.
2. Description of the Related Art
A conventional belt sander comprises a frame, an upper roller mounted on an upper end of the frame, a lower roller mounted on a lower end of the frame, and a sand belt mounted between the upper roller and the lower roller. Thus, the sand belt is driven by the upper roller and the lower roller to rotate at a high speed to grind a workpiece, such as a wooden material.
In practice, when the workpiece touches the sand belt, the workpiece is accelerated by the pulling force of the sand belt. When the workpiece is grinded by the sand belt, the workpiece is moved forward smoothly by friction and resistance of the sand belt. When the workpiece is about to leave the sand belt, the resistance applied on the workpiece by the sand belt is removed, so that the workpiece is accelerated to move forward. However, the workpiece is not moved forward at a constant during the grinding process, thereby greatly decreasing the grinding effect and the quality of the workpiece.